Inclusion Criteria:

          -  Previously untreated (no local therapy such as surgery, radiation cryotherapy, HIFU,
             etc.) localized adenocarcinoma of the prostate with the following clinical findings:

               -  Clinical stage by digital rectal exam of either T1c or T2a/b (limited to one side
                  of the gland); (American Joint Committee on Cancer [AJCC], version 7) or cT1a-c
                  or 2a or 2b,

               -  Stages T1a-T1b are eligible if patient underwent transurethral prostatic
                  resection (TURP),

               -  The patient must meet one of the following 3 criteria: 1) Gleason score must be
                  Gleason 7(3+4) with a PSA < 20 ng/mL, or 2) Gleason 6(3+3) with a PSA > 10 ng/mL
                  and < 20 ng/mL; (AJCC, version 7) or 3) Group Grade 1 or 2

                    -  If patient is receiving a 5-alpha reductase inhibitor at the time of
                       enrollment the baseline PSA value may be double the initial value and the
                       medication should be discontinued but a washout period is not required to
                       eligible, a PSA drawn while still on the medicine must be:

                         -  < 10 ng/mL if Gleason 7(3+4) (Note: This patient would be on
                            stratification level 1 if PSA < 5 ng/mL and stratification level 2 if
                            less than 10 ng/mL).

                         -  > 5 ng/mL and less than 10 ng/mL for Gleason 6(3+3) (Note: This
                            patients would be on stratification level 3).

               -  The prostate volume must be < 70 cc as reported at time of biopsy or by separate
                  measure with ultrasound or other imaging modalities including magnetic resonance
                  imaging (MRI) or computed tomography (CT) scan

               -  Patients in active surveillance who elect to be treated are eligible if they meet
                  protocol requirements

          -  History and physical including a digital rectal exam 60 days prior to registration

          -  Eastern Cooperative Oncology Group (ECOG) performance status 0-1 60 days prior to
             registration

          -  MRI of the prostate and pelvis (compliant with PIRADSv2.1 guidelines) within 1 year
             prior to registration

          -  Bone scan or sodium fluoride positron emission tomography (PET) scan within 120 days
             prior to registration

          -  Charlson modified co-morbidity score =< 4 for patients under 60 and =< 5 for patients
             60 and over 21 days prior to registration

          -  International prostate symptom score (IPSS) of < 15 21 days prior to registration

          -  The patient must provide study-specific informed consent prior to study entry

          -  Willingness and ability to complete the Expanded Prostate Cancer Index Composite
             (EPIC-26) questionnaire

          -  Completion of all items of the EPIC-26 which will be data entered at registration 60
             days prior to registration

          -  Only English, Spanish, and French-speaking patients are eligible to participate

        Exclusion Criteria:

          -  Definitive clinical or radiologic evidence of metastatic disease; no nodal involvement
             or evidence of metastatic disease allowed as defined by screening of the pelvis and a
             bone scan or sodium fluoride PET scan

          -  Definitive T3 disease on MRI

          -  Prior or current invasive malignancy with current evidence of active disease within
             the past 2 years

               -  Exceptions: Non-melanomatous skin cancer, carcinoma in situ of the male breast,
                  penis, oral cavity, or stage Ta of the bladder, or stage I completely resected
                  melanoma.

          -  Prior systemic chemotherapy for the study cancer; note that prior chemotherapy for a
             different cancer is allowable; must be off treatment for at least 3 years

          -  Prior radiotherapy to the region of the study cancer that would result in overlap of
             radiation therapy fields

          -  The use of hormonal therapy is not allowed; if the patient in on a 5-alpha reductase
             inhibitor, then they should be stopped prior to treatment once enrolled onto the
             study; no washout period is required for this study to participate

          -  Severe, active co-morbidity defined as follows:

               -  Human immunodeficiency virus (HIV) positive with CD4 count < 200
                  cells/microliter; Note that patients who are HIV positive are eligible, provided
                  they are under treatment with highly active antiretroviral therapy (HAART) and
                  have a CD4 count >= 200 cells/microliter within 30 days prior to registration;
                  Note also that HIV testing is not required for eligibility for this protocol

               -  Hepatic insufficiency resulting in clinical jaundice and/or coagulation defects;
                  note, however, that laboratory tests for liver function and coagulation
                  parameters are not required for entry into this protocol; (patients on Coumadin
                  or other blood thinning agents are eligible for this study)

          -  Contraindication to MRI

               -  Cardiac pacemaker or defibrillator

               -  Surgically implanted electrical devices such as spinal stimulation devices or
                  intracranial stimulation devices, cochlear implants, the presence of metallic
                  foreign bodies in the orbits, and incompatible old mechanical heart valves and
                  aneurysm clips